1. Field of the Invention
The present invention generally relates to a semiconductor device as a rectify element incorporated in a rectify device to be applied to a vehicle alternator mounted on a vehicle such as a passenger car and a truck.
2. Description of the Related Art
A vehicle alternator is driven by the engine power generated by and transmitted from an internal combustion engine mounted on a vehicle in order to generate electric power. The vehicle alternator supplies the generated electric power to a battery, and the battery charges the electric power therein. The vehicle alternator also supplies the generated electric power to various kinds of electric devices and loads mounted on the vehicle such as an igniter for the internal combustion engine, a lighting system and auxiliaries.
In order to maintain and further strengthen the competitive power in the international market, it is necessary to achieve downsizing of a vehicle alternator and drastic cost-down of the manufacturing cost, and to increase or enhance the magnitude of its output power and reliability. Those are the important problems to be solved at present in such a technical field. For example, in order to increase the reliability and lifetime of a rectify element as a semiconductor device, the press-in mechanism and its manner has been known. The semiconductor device as the rectify element on which a semiconductor chip is fabricated is press-in into a hole section formed in a radiating fin of the rectify device in order to adequately and efficiently radiate the heat generated in the semiconductor chip because a large amount of current flows therein. The Japanese laid open publication (No. JP 2002-119029) has disclosed such a conventional semiconductor device as the rectify element incorporating a semiconductor chip. Such a semiconductor device has a disk section in which a concave part is formed. The semiconductor chip is placed on and fixed to the bottom of the concave part with solder. The outside peripheral wall of the disk section in the semiconductor device has a cylindrical or tubular shape and the side wall of the concave part that is faced to the inside peripheral wall of the disk section also has a cylindrical shape. The side wall of the concave part is perpendicular to the bottom surface of the disk section of the semiconductor device. After the completion of the solder process of the semiconductor chip, the semiconductor chip is sealed with a silicon rubber or resin as a sealing member in the concave part.
In general, a vehicle alternator is equipped with such a rectify device disclosed in the above patent document, and the armature shaft of the vehicle alternator is mounted on the vehicle in parallel to the surface of the ground. Such a case, because the bottom surface of the disk section of the semiconductor device is disposed perpendicular to the surface of the ground, the side wall of the concave part in the disk section is perpendicular to the bottom surface or the inside upper surface of the disk section. That means that the inside wall of the concave part is placed in parallel to the surface of the ground. Accordingly, if the sealing member is separated from the concave part in the disk section by erosion of moisture, water, or salt water, and the water or moisture is then accumulated in the concave part, the water or moisture ingress occurs. The water or moisture accumulated in the concave part, and then reaches to the semiconductor chip formed in the concave part and formed on the disk section. Thus, the semiconductor device involves various drawbacks, for example, the semiconductor chip falls in short circuit by water, moisture, or salt water ingress, and its reliability deteriorates and its lifetime is further decreased, or the semiconductor device thereby falls in failure.